Injection of solutions into balloon catheters to inflate the balloons is conducted hundreds of thousands of times every year. This invention addresses the need to monitor inflation pressures in angioplasty balloon catheters. In angioplasty, a catheter is maneuvered into the obstructed blood vessel or any other obstructed tract and a balloon at the tip of the catheter is inflated to compress plaque or alleviate strictures. During such procedures, physicians require the ability to monitor pressure applied within the balloon for safety and efficacy related reasons.
Angioplasty, or balloon dilatation, was introduced by the late Dr. A. Gruntzig in the early seventies. The approach utilized the concept of a dilatation catheter. A catheter is a hollow polymeric (i.e., polyurethane, polyvinylchloride, polyethylene, etc.) tube, sometimes designed with multiple lumens to facilitate infusions or pressure monitoring, or with braided wire support in the catheter wall to improve its torque control or "steerability." A dilatation catheter is a specifically designed catheter with a high strength balloon at its tip.
The most common application of angioplasty is in the coronaries. The percutaneous transluminal coronary angioplasty (PTCA) procedure involves: (a) an introducer sheath; (b) a guiding catheter; (c) a balloon catheter; (d) a steerable guide wire; (e) radiologic equipment; (f) monitoring equipment; (g) manifolds, valves, adaptors and tubing assembled by the operator to form an infusion system; and (h) an inflation device and pressure gauge to inflate and deflate the balloon to desired pressures to affect dilatation.
Three key requirements that hold throughout such procedures are: (i) the biocompatibility and nonpyrogenecity of all components that can possibly come in contact with the patient's tissue or blood, including such components that may come in contact with solutions that eventually may contact body tissue or blood; (ii) the total freedom of the whole system from any air bubbles which, if somehow allowed within the body, can cause embolisms with injurious or fatal consequences; and (iii) the ability to monitor inflation pressures accurately, including negative pressure generated by partial vacuum in the fluid lines.
So far, the above-mentioned medical requirements have been observed steadfastly, except in the case of pressure gauges used in such procedures. Such mechanisms have not been made biocompatible, nonpyrogenic or safe from gas bubble entrapments to the extent necessary by the nature of the application. Generally speaking, there are three widely used types of mechanical pressure gauge mechanisms, as discussed below.